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Slide 1 of 30
Copyright Pearson Prentice Hall
Biology
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23-5 Transport in Plants
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23-5 Transport in Plants
Slide 3 of 30
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Water Pressure
Water Pressure
Xylem tissue forms a continuous set of tubes that runs from the roots through stems and out into the spongy mesophyll of leaves.
Active transport and root pressure cause water to move from soil into plant roots.
Capillary action and transpiration also are needed to transport water and minerals.
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23-5 Transport in Plants
Slide 4 of 30
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Water Pressure
How is water transported throughout a plant?
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23-5 Transport in Plants
Slide 5 of 30
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Water Pressure
The combination of root pressure, capillary action, and transpiration provides enough force to move water through the xylem tissue of even the tallest plant.
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23-5 Transport in Plants
Slide 6 of 30
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Water Pressure
Cohesion is the attraction of molecules of the same substance to each other.
Adhesion is the attraction between unlike molecules.
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23-5 Transport in Plants
Slide 7 of 30
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Water Pressure
The tendency of water to rise in a thin tube is called capillary action.
Water is attracted to the walls of the tube, and water molecules are attracted to one another.
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23-5 Transport in Plants
Slide 8 of 30
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Water Pressure
Capillary action causes water to move much higher in a narrow tube than in a wide tube.
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23-5 Transport in Plants
Slide 9 of 30
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Water Pressure
Tracheids and vessel elements form hollow connected tubes in a plant.
Capillary action in these structures causes water to rise well above the level of the ground.
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23-5 Transport in Plants
Slide 10 of 30
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Water Pressure
Transpiration
In tall plants, the major force in water transport comes from the evaporation of water from leaves during transpiration.
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23-5 Transport in Plants
Slide 11 of 30
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Water Pressure
When water is lost through transpiration, osmotic pressure moves water out of the vascular tissue of the leaf.
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23-5 Transport in Plants
Slide 12 of 30
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Water Pressure
The movement of water out of the leaf “pulls” water upward through the vascular system all the way from the roots.
This process is known as transpirational pull.
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23-5 Transport in Plants
Slide 13 of 30
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Water Pressure
Controlling Transpiration
The water content of the leaf is kept relatively constant.
When there is a lot of water, water pressure in the guard cells is increased and the stomata open.
Excess water is then lost through the open stomata by transpiration.
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23-5 Transport in Plants
Slide 14 of 30
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Water Pressure
When water is scarce, the opposite occurs.
Water pressure in the leaf decreases. The guard cells respond by closing the stomata.
This reduces further water loss by limiting transpiration.
When too much water is lost, wilting occurs. When a leaf wilts, its stomata close and transpiration slows down. This helps a plant conserve water.
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23-5 Transport in Plants
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Nutrient Transport
How are the products of photosynthesis transported throughout a plant?
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23-5 Transport in Plants
Slide 16 of 30
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Nutrient Transport
Nutrient Transport
Many plants pump sugars into their fruits.
In cold climates, plants pump food into their roots for winter storage.
This stored food must be moved back into the trunk and branches of the plant before growth begins again in the spring.
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23-5 Transport in Plants
Slide 17 of 30
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Nutrient Transport
Movement from Source to Sink
A process of phloem transport moves sugars through a plant from a source to a sink.
A source is any cell in which sugars are produced by photosynthesis.
A sink is any cell where the sugars are used or stored.
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23-5 Transport in Plants
Slide 18 of 30
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Nutrient Transport
When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of fluid in that same direction.
As a result, phloem is able to move nutrients in either direction to meet the nutritional needs of the plant.
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23-5 Transport in Plants
Slide 19 of 30
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Nutrient Transport
One idea that explains how phloem transport takes place is called the pressure-flow hypothesis.
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23-5 Transport in Plants
Slide 20 of 30
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Nutrient Transport
Sugars produced during photosynthesis are pumped into the phloem (source).
Sugar molecules
Movement of water
Movement of sugar
Phloem Xylem
Source cell
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23-5 Transport in Plants
Slide 21 of 30
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Nutrient Transport
As sugar concentrations increase in the phloem, water from the xylem moves in by osmosis.
Movement of water
Movement of sugar
Sugar molecules
Phloem Xylem
Source cell
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23-5 Transport in Plants
Slide 22 of 30
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Nutrient Transport
Movement of water
Movement of sugar
This movement causes an increase in pressure at that point, forcing nutrient-rich fluid to move through the phloem from nutrient-producing regions ….
Sugar molecules
Phloem Xylem
Source cell
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23-5 Transport in Plants
Slide 23 of 30
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Nutrient Transport
…. toward a region that uses these nutrients (sink).
Xylem Phloem
Movement of water
Movement of sugar
Sink cell
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23-5 Transport in Plants
Slide 24 of 30
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Nutrient Transport
If part of a plant actively absorbs nutrients from the phloem, osmosis causes water to follow.
This decreases pressure and causes a movement of fluid in the phloem toward the sink.
Movement of water
Movement of sugar
Xylem Phloem Sink cell
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Slide 25 of 30
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23–5
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Slide 26 of 30
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23–5
In a plant stem, water moves from
a. leaves to roots through xylem.
b. roots to leaves through xylem.
c. leaves to roots through phloem.
d. roots to leaves through phloem.
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Slide 27 of 30
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23–5
Which of the following is NOT involved in the movement of water in xylem tissue?
a. cohesion
b. osmosis
c. capillary action
d. adhesion
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Slide 28 of 30
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23–5
When nutrients are pumped into the phloem system of a plant, the increased concentration
a. causes fluid to move into the system.
b. causes fluid to move out of the system.
c. has no effect on the movement of fluid.
d. causes fluid to move into the xylem vessels.
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Slide 29 of 30
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23–5
In a plant, sugar is moved from source cells to sink cells by a process of
a. phloem transport.
b. xylem transport.
c. osmosis.
d. diffusion.
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Slide 30 of 30
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23–5
In very tall trees, which of the following is primarily involved in moving water to the top of the tree?
a. transpirational pull
b. capillary action
c. root pressure
d. osmosis
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